1. Field of the Invention
The present invention relates to a visible-light communication system, and more particularly to a visible-light communication system in which a user can identify the state of a communication channel in real time during data reception mode.
2. Description of the Related Art
In general, a wireless mobile communication terminal is equipped to display, a received signal strength in a predetermined position of a display unit so as to provide a received signal strength indication (RSSI) signal from a base station in real time. FIG. 1 is a block diagram illustrating the configuration of a wireless mobile communication terminal displaying the reception intensity according to the conventional wireless communication scheme. When a wireless mobile communication terminal is powered on, a wireless transmission/reception unit 100 transfers an RSSI signal received from an exterior in a scheme according to a wireless communication standard. The RSSI signal is defined as a voltage level, and is input to a wireless controller 110. The voltage level of the input RSSI signal is converted into a digital signal by an A/D converter 111, and then stored in a temporary RSSI storage unit 112, which is a specified register. The stored RSSI is used to provide the current state of a wireless communication to a user using antenna bars in a display unit 120.
FIG. 2 is a view schematically illustrating a data transmission scheme of a data link layer in a conventional wireless communication system using infrared rays. According to the infrared link access protocol (IrLAP) of the infrared data association (IrDA), a sender transmits data to a receiver, and then the receiver transmits an Acknowledge (ACK) signal in response to the transmitted data, as shown FIG. 2. Generally, when a window size, representing the number of packets or frames which a sender can consecutively transmit through a communication channel without waiting for an Acknowledge (ACK) signal from a receiver, is one, the receiver must transmit an ACK signal as a response whenever receiving this one data frame. The IrDA allows the window size to be a maximum of 128, so that it is possible increase the throughput of data. However, the IrDA using infrared rays have disadvantages in that it takes a long time to transmit contents because a data rate is limited to a few Mbps, and the user cannot visibly identify the state of a communication channel. For these reasons stated above, a visible-light communication system using visible light has been recently spotlighted because the visible-light communication system can achieve low-power high-speed communication at a low price by constructing a communication channel using an element, such as a light emitting diode (LED). The implementation of LED is noted as an ideal choice in the next generation. Such a visible LED serves as an access point (AP) in a visible-light communication system. Since it is possible to perceive the visible light, which is a communication medium, owing to the visible characteristic of the visible light, (e.g. a space illuminated by a room lamp), a user can easily recognize a range to which the visible light reaches.
That is, when an LED is installed in a room provided with a conventional bulb lighting, a visible-light communication system can be easily implemented without installing an additional system as LED visible light communication is possible.
In the visible light communication, information is transmitted by switching on and off the light emitted from a light emitting diode as an indicator at a high speed. Thus, when a terminal, such as a PC, is installed within a range which light can reach, it is possible to use high-speed Internet communication or the like, without wiring.
As shown in FIGS. 1 and 2, according to the conventional wireless communication technology using an RF or the conventional technology using infrared rays, since the current state of a communication channel is displayed simply using antenna bars, and an Acknowledge signal or Negative Acknowledge signal, representing whether data has been successfully received, cannot be generated and transmitted before the reception of the data has been completed. Also, the user cannot identify a channel state and a data rate in real time while data is being received. Therefore, there is a need to develop an improved communication protocol applicable to a visible-light communication system.